How Pregnancy Test Works - Why It Fails At Times

Appearance of the five early signs of pregnancy requires the confirmation of pregnancy through the pregnancy test which can be done at home using the test kits or strips available in the medical stores. How and when this test should be done has been discussed in detail in the previous post. Today, let's see how this pregnancy test works and what is the principle involved.

How Pregnancy Test Works? - Principle Involved

Urine test or the blood test employed in diagnosing pregnancy works by detecting a particular hormone called HCG in the urine or blood sample obtained from a pregnant woman.

About HCG

Human Chorionic Gonadotrophin, i.e., HCG is produced by the cells of the placenta and secreted into both maternal and fetal blood and is necessary for sustaining pregnancy.

• At the earliest, it can be detected in the serum or urine of the mother, 8 to 9 days after ovulation.

• Its amount reaches maximum level between 60 to 70 days of pregnancy after which its concentration falls till 100 to 130 days.

• Thereafter HCG level remains constant with a slight rise at 32 week.

• Two weeks after child birth, HCG disappears from the mother's body.

Why Pregnancy Test Is False Negative Sometimes?

The test results are mostly accurate when performed at the correct time following the instructions mentioned in the previous post - How To Do Pregnancy Test At Home?

Reasons for a negative test may be:

#1. If the urine sample is too dilute, HCG level may not be detected.

#2. If the test is performed too early, the low levels of HCG cannot be detected.

#3. Test done after 12 weeks of pregnancy will not detect HCG.

#4. If you have not followed the instructions properly, you may get an incorrect result.

Why Pregnancy Test Is False Positive Sometimes?

A test may show positive result in a non-pregnant woman if:

#1. Test has not been performed in a correct manner.

#2. Using an expired kit or strip for the test.

#3. Test results not read within 3-5 minutes.

#4. HCG injection is given to the woman as a part of infertility treatment.

#5. Certain diseases such as choriocarcinoma, germ cell tumor etc. may also produce a false positive result.


#6. Use of antipsychotic drugs and sedatives.


#7.  More conditions which may cause false positive results include:

• Hypothyroidism 
• Menopausal woman
• Renal failure
• Oophorectomy(ovaries have been removed)

After detecting pregnancy through the home test kits or in case of any doubt you should visit your gynaecologist for further confirmation and monitoring of pregnancy through ultrasound .

Also read:
How To Know If You Are Pregnant - 5 Early Signs
How And When To Do Pregnancy Test At Home

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